Evaluation of the Tibial Plateau-Patella Angle (TPPA) in Dogs

Estimating a dog's patellar position involves various methods, which categorize it as norma, alta (high), or baja (low). However, they require various calculations. We aimed to evaluate the clinical applicability of a new method, the tibial plateau-patella angle (TPPA). This could aid in planning patella luxation surgery, estimating the patella position after TPLO and various osteotomies. We conducted a two-step study: first, on 15 stifles without pathologies from nine canine cadavers, and second, using 100 patient X-rays from the archive. Three stifle angle positions (45 ± 5°, 90 ± 5°, and 135 ± 5°) and three weight groups (S, M, and L) were evaluated in the first part of this study. Based on these results, the second part of this study was conducted using 100 pathology-free radiographs at the optimal stifle angle (90 ± 5°) from the archive. All radiographs were measured by three observers with varying levels of experience. Our results indicate that the stifle angle significantly impacted the TPPA, whereby lower values were detected with higher stifle angles, which remained consistent within the weight groups. High inter- and intra-observer agreement was achieved. The physiological TPPA values ranged from 26.7° to 48.8°, remaining consistent within the various weight groups. Observer 3 in Group S exhibited a 20% (insignificant) deviation, possibly due to challenges in determining the caudal point of the tibial plateau. In contrast with humans, TPPA values in dogs are negatively correlated with stifle angles, independent of weight. Our reliable and reproducible protocol suggests the potential benefits of training on small-breed dogs stifles.